Lecture - development

Question 1

Embryos consist of three layers of tissue

Answer 1

ectoderm (outermost), mesoderm (middle), and endoderm (innermost).

Question 2

phases of development

Answer 2

induction of the neural plate; neural proliferation; migration and aggregation; axon growth and synapse formation; and neuron death and synapse rearrangement.

Question 3

induction of the neural plate

Answer 3

A patch of tissue on the ectoderm becomes the neural plate. This transformation is induced by chemical signals from the mesoderm. Visible three weeks after conception.

Question 4

embryonic stem cells

Answer 4

neural plate cells. have unlimited capacity for self renewal. can become any type of mature cell.

Question 5

totipotent

Answer 5

earliest cells have the ability to become any type of body cell

Question 6

Multipotent

Answer 6

with development, neural plate cells are limited to becoming one of the range of mature nervous system cells

Question 7

neural crest

Answer 7

A structure dorsal to the neural tube and formed from neural tube cells. Develops into the cells of the peripheral nervous system.

Question 8

neural proliferation

Answer 8

Neural plate folds to form the neural groove, which then fuses to form the neural tube. The neural tube will become the cerebral ventricles and central canal in the spinal cord. Neural tube cells proliferate forming three swellings: forebrain, midbrain, and hindbrain.

Question 9

neural migration

Answer 9

Once cells have been created through cell division in the ventricular zone of the neural tube, they migrate to their final destinations to form nuclei and cortical layers. Migrating cells are immature, lacking axons and dendrites.

Question 10

cortical layers form in an

Answer 10

“inside out pattern.” layer 6 forms first, then 5, 4, etc.

Question 11

two types of neural tube migration

Answer 11

radial migration and tangential migration. most cells engage in both types.

Question 12

radial migration

Answer 12

usually by moving along radial glial cells

Question 13

two methods of migration

Answer 13

somal - caterpillar-like

glial-mediated migration - – cell moves along a radial glial network

Question 14

neural aggregation

Answer 14

After migration, cells align themselves with others cells and form nuclei.

Question 15

neural differentiation

Answer 15

Neurons take their adult morphology

Question 16

myelination

Answer 16

In humans, starts in spinal cord and continues toward forebrain

Question 17

growth cone

Answer 17

At the growing tip of each axon, the growth cone

extends and retracts filopodia as if exploring to find its way

Question 18

1. blueprint hypothesis (for target finding and synapse info)

Answer 18

pre-formed pathways and tunnels.

• Pioneer growth cones, guidepost cells, fasciculation.
• Role of cell-adhesion molecules (CAM).
• Evidence against: Cells transplanted to other places still find correct targets.

Question 19

2. chemoaffinity hypothesis (for target finding and synapse info)

Answer 19

Connections are

highly specific. Sperry’s eye rotation experiment.

Question 20

topographic gradient hypothesis

Answer 20

sheets of developing neurons are often charcterized by two intersecting chemical gradients, which can define the localization of each neuron.

Question 21

3. fine-tuning of connections by spontaneous and experience-evoked neural activity (for target finding and synapse info)

Answer 21

• The Hebb postulate: Neurons that fire together, wire together.
• N-methyl-D-aspartate receptors (NMDA receptors) detect correlated activity between pre- and post-synaptic neurons

Question 22

overproduction

Answer 22

during development many neurons die.

Question 23

apoptosis

Answer 23

active, programmed cell death

Question 24

necrosis

Answer 24

passive cell death.

Question 25

Neurons die due to failure to

Answer 25

compete for neurotrohic factors provided by targets (e.g., NGF, nerve growth factor). the more targets, the fewer cell deaths. destroying some cells increases survival rate of remaining cells.

Question 26

synapse rearrangemnet

Answer 26

a diffuse pattern of synaptic contact is characteristic of early stages of devleopment. a more focused pattern of synaptic contact is present after synapse rearrangment.

Question 27

More than 200 genetic mutations

Answer 27

associated with mental retardation

Question 28

Developing brain is more vulnerable than the mature brain to

Answer 28

malnutrition, toxic chemicals and infections.

Question 29

Hypothyroidism

Answer 29

induces mental retardation in infants.

Question 30

fetal alcohol syndrome

Answer 30

Dendrites tend to be short, with few branches

Question 31

rett syndrome

Answer 31

Anomaly of brain development with mental retardation affecting mainly girls older than 1-2 years. Associated with lack of dendritic development.